Joseph:

There is a high degree of possibility that connecting a port pin that is currently programmed to a LOW output to +VDD through a switch would cause irreversable damage to the microcontroller. The connection would have to be maintained long enough to permit the damage to occur through excessive temperature rise of the chip or outright fusing of the chip bonding wires or the port pin output low transistor. The ON resistance of the output low transistor is something greater than zero ohms and so you will not see unlimited current flow at the time the switch is closed. As a matter of fact a momentary short may not actually do any damage to the part at all.

You are correct in the assertion that hardware and/or software debouncing needs to (and should) be done in this type application to ensure that the SMS string transmission only occurs once per "user press" of the switch and not once per "bounce" of the switch. I almost posted a re-vamp of Martina Murphy's main routine with a debounce provision included...however decided not to because....

1) I saw that debounce had been suggested

and

2) I thought "What better way to learn about the need for debounce" if the original poster to trys out the program with the simple while(SWT) and while(!SWT) logic in it.

Michael Karas